Real Time and In-Situ Spectroscopic Ellipsometry of CuyIn1−xGaxSe2 for Complex Dielectric Function Determination and Parameterization

  • Abdel-Rahman A. Ibdah
  • Puruswottam Aryal
  • Puja Pradhan
  • Sylvain Marsillac
  • Nikolas J. PodrazaEmail author
  • Robert W. Collins
Part of the Springer Series in Optical Sciences book series (SSOS, volume 212)


Real time spectroscopic ellipsometry (RTSE) has been applied to characterize the structural evolution and final structural properties of ~50–60 nm thin film Cuy(In1−xGax)Se2 (CIGS) solar cell absorber layers deposited by single stage co-evaporation onto crystalline silicon wafer substrates. Two series of depositions were explored; the first spans the range of copper atomic fraction y = [Cu]/([In] + [Ga]) of 0.45 < y < 1.20 for fixed gallium atomic fraction x = [Ga]/([In] + [Ga]) = 0.30 and the second spans the range of 0 ≤ x < 0.50 with fixed y ~ 0.90, as measured by energy dispersive X-ray spectroscopy. Systematic variations in the structural evolution with y reveal that near stoichiometric films undergo significant roughening typically associated with crystallite nucleation and growth whereas films with low and high Cu contents undergo significant smoothening during coalescence typically associated with disordered films or surface regions. The final film structural parameters determined from RTSE enable accurate determination of complex dielectric functions at the deposition temperature and at room temperature based on in-situ SE measurements performed immediately after the deposition process and after film cooling, respectively. Critical point (CP) analysis applying a standard lineshape was performed by fitting twice differentiated dielectric functions. Thus, the resulting CP resonance energies were obtained in accordance with the standardized procedures developed for research on the optical properties of semiconductors. An analytical expression describing the complex dielectric functions of the CIGS films over the range 0.75–3.8 eV was developed that incorporates photon energy independent parameters associated with four CP resonances, a modified Lorentz oscillator as a broad background between CPs, and a sub-bandgap Urbach tail. The procedure for fitting the dielectric functions by this expression was stabilized by fixing the CP energies deduced in the CP analysis. Polynomials describing the dependence on the Cu content y and the Ga content x for each of the photon energy independent parameters were obtained by fitting the plots of these parameter values as functions of y and x. The utility of the dielectric function expression and associated polynomials has been demonstrated through ex-situ spectroscopic ellipsometry (SE) applications in which the compositional parameters of x and y for a ~450 nm CIGS film have been mapped over a 10 cm × 10 cm sample area. Although the dielectric functions have been deduced from ~50–60 nm films on ideal smooth substrates, they have been effective in serving as a database for compositional analysis of much thicker films, as well as films on Mo coated glass substrates in the solar cell configuration.


  1. 1.
    W.N. Shafarman, S. Siebentritt, L. Stolt, in Handbook of Photovoltaic Science and Engineering, ed. by A. Luque, S. Hegedus, 2nd edn. (Wiley, New York, NY, 2011), Chapter 13, p. 546Google Scholar
  2. 2.
    T.-P. Hsieh, C.-C. Chuang, C.-S. Wu, J.-C. Chang, J.-W. Guo, W.-C. Chen, in Proceedings of the 34th IEEE Photovoltaics Specialists Conference (PVSC), June 7–12, 2009, Philadelphia, PA (IEEE, New York, NY, 2009), p. 886Google Scholar
  3. 3.
    C. Stephan, Structural Trends in Off Stoichiometric Chalcopyrite Type Compound Semiconductors. Ph.D. Dissertation, Freie Universität Berlin, Helmholtz-Zentrum Berlin, Germany, 2011Google Scholar
  4. 4.
    M. Powalla, W. Witte, P. Jackson, S. Paetel, E. Lotter, R. Würz, F. Kessler, C. Tschamber, W. Hempel, D. Hariskos, R. Menner, A. Bauer, S. Spiering, E. Ahlswede, T. Magorian Friedlmeier, D. Blazquez-Sanchez, I. Klugius, W. Wischmann, IEEE J. Photovolt. 4, 440 (2014)CrossRefGoogle Scholar
  5. 5.
    A.-R. Ibdah, Optical Physics of Cu(In, Ga)Se2 Solar Cells and Their Components. Ph.D. Dissertation, University of Toledo, Toledo, OH, USA, 2017Google Scholar
  6. 6.
    P. Aryal, Optical and Photovoltaic Properties of Copper Indium-Gallium Diselenide Materials and Solar Cells. Ph.D. Dissertation, University of Toledo, Toledo, OH, USA, 2014Google Scholar
  7. 7.
    P. Aryal, A.-R. Ibdah, P. Pradhan, D. Attygalle, P. Koirala, N.J. Podraza, S. Marsillac, R.W. Collins, J. Li, Prog. Photovolt.: Res. Appl. 24, 1200 (2016)CrossRefGoogle Scholar
  8. 8.
    J.D. Walker, H. Khatri, V. Ranjan, S. Little, R. Zartman, R.W. Collins, S. Marsillac, in Proceedings of the 34th IEEE Photovoltaic Specialists Conference (PVSC), 7–12 June 2009, Philadelphia, PA (IEEE, New York, NY, 2009), p. 1154Google Scholar
  9. 9.
    R.W. Collins, A.S. Ferlauto, in Handbook of Ellipsometry, ed. by H.G. Tompkins, E.A. Irene, (William Andrew, Norwich, NY, 2005), Chapter 2, p. 93Google Scholar
  10. 10.
    W.G. Oldham, Surf. Sci. 16, 97 (1969)ADSCrossRefGoogle Scholar
  11. 11.
    I. An, Y.M. Li, H.V. Nguyen, C.R. Wronski, R.W. Collins, Appl. Phys. Lett. 59, 2543 (1991)ADSCrossRefGoogle Scholar
  12. 12.
    S. Marsillac, V. Ranjan, S. Little, R.W. Collins, in Proceedings of the 35th IEEE Photovoltaic Specialists Conference (PVSC), 20–25 June 2010, Honolulu, HI (IEEE, New York NY, 2010), p. 866Google Scholar
  13. 13.
    V. Ranjan, R.W. Collins, S. Marsillac, Phys. Stat. Sol. RRL 6, 10 (2012)CrossRefGoogle Scholar
  14. 14.
    P. Pradhan, P. Aryal, A.-R. Ibdah, K. Aryal, J. Li, N. J. Podraza, S. Marsillac, R.W. Collins, in Proceedings of the 40th IEEE Photovoltaics Specialists Conference (PVSC), 8–13 June 2014, Denver, CO (IEEE, New York, NY, 2014), pp. 2060–2065Google Scholar
  15. 15.
    M.A. Contreras, J. Tuttle, A. Gabor, A. Tennant, K. Ramanathan, S. Asher, A. Franz, J. Keane, L. Wang, J. Scofield, R. Noufi, Proceedings of the First World Conference on Photovoltaic Energy Conversion, 5–9 Dec 1994, Waikoloa, HI (IEEE, New York, 1994), p. 68Google Scholar
  16. 16.
    H. Liu, X. Shi, F. Xu, L. Zhang, W. Zhang, L. Chen, Q. Li, C. Uher, T. Day, G.J. Snyder, Nature Mat. 11, 422 (2012)ADSCrossRefGoogle Scholar
  17. 17.
    J. Koh, A.S. Ferlauto, P.I. Rovira, C.R. Wronski, R.W. Collins, Appl. Phys. Lett. 75, 2286 (1999)ADSCrossRefGoogle Scholar
  18. 18.
    P. Pradhan, D. Attygale, P. Aryal, N.J. Podraza, A.S. Ferlauto, S. Marsillac, R.W. Collins, Proceedings of the 39th IEEE Photovoltaics Specialists Conference, 16–21 June 2013, Tampa, FL (IEEE, New York, NY, 2013), p. 414Google Scholar
  19. 19.
    S. Siebentritt, L. Gütay, D. Regesch, Y. Aida, V. Deprédurand, Sol. Ener. Mater. Sol. Cells 119, 18 (2013)CrossRefGoogle Scholar
  20. 20.
    S. Minoura, T. Maekawa, K. Kodera, A. Nakane, S. Niki, H. Fujiwara, J. Appl. Phys. 117, 195703 (2015)ADSCrossRefGoogle Scholar
  21. 21.
    M.I. Alonso, M. Garriga, C.A. Durante Rincón, E. Hernández, M. León, Appl. Phys. A 74, 659 (2002)ADSCrossRefGoogle Scholar
  22. 22.
    S. Minoura, K. Kodera, T. Maekawa, K. Miyazaki, S. Niki, H. Fujiwara, J. Appl. Phys. 113, 063505 (2013)ADSCrossRefGoogle Scholar
  23. 23.
    A.S. Ferlauto, G.M. Ferreira, J.M. Pearce, C.R. Wronski, R.W. Collins, X.M. Deng, G. Ganguly, J. Appl. Phys. 92, 2424 (2002)ADSCrossRefGoogle Scholar
  24. 24.
    P. Aryal, D. Attygalle, P. Pradhan, N.J. Podraza, S. Marsillac, R.W. Collins, IEEE J. Photovolt. 3, 359 (2013)CrossRefGoogle Scholar
  25. 25.
    N.J. Podraza, C.R. Wronski, M.W. Horn, R.W. Collins, in Amorphous and Polycrystalline Thin-Film Silicon Science and Technology—2006, Materials Research Society Symposium Proceedings, vol. 910, ed. by S. Wagner, V. Chu, H.A. Atwater, K. Yamamoto, H.-W. Zan, (MRS, Warrendale, PA, 2006), p. 259Google Scholar
  26. 26.
    J. Li, N.J. Podraza, R.W. Collins, Phys. Stat. Sol (a) 205, 901 (2008)ADSCrossRefGoogle Scholar
  27. 27.
    P. Aryal, J. Chen, Z. Huang, L.R. Dahal, M.N. Sestak, D. Attygalle, R. Jacobs, V. Ranjan, S. Marsillac, R.W. Collins, in Proceedings of the 37th IEEE Photovoltaics Specialists Conference, 19–24 June 2011, Seattle, WA (IEEE, New York NY, 2011), p. 2241Google Scholar
  28. 28.
    A. Nakane, H. Tampo, M. Tamakoshi, S. Fujimoto, K.M. Kim, S. Kim, H. Shibata, S. Niki, H. Fujiwara, J. Appl. Phys. 120, 064505 (2016)ADSCrossRefGoogle Scholar
  29. 29.
    A.-R. Ibdah, P. Koirala, P. Aryal, P. Pradhan, S. Marsillac, A.A Rockett, N.J. Podraza, R.W. Collins, Appl. Surf. Sci. (2017). Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Abdel-Rahman A. Ibdah
    • 1
  • Puruswottam Aryal
    • 1
  • Puja Pradhan
    • 1
  • Sylvain Marsillac
    • 2
  • Nikolas J. Podraza
    • 1
    Email author
  • Robert W. Collins
    • 1
  1. 1.Department of Physics & Astronomy and Center for Photovoltaics Innovation & CommercializationUniversity of ToledoToledoUSA
  2. 2.Virginia Institute of Photovoltaics, Old Dominion UniversityNorfolkUSA

Personalised recommendations